Technological developments have allowed computer networks to be faster and less costly, and accordingly video transmission over a network is becoming widespread. Terminals for receiving video transmission also has further diversified, and electrical home appliances equipped with Internet access functions, namely televisions and DVRs (digital video recorders), have been developed in addition to mobile phones and personal computers. From now on, electrical home appliances are likely to receive, display, and record video stream data transmitted over the Internet.
The above environment where the diversified devices can severally display video images received through a network allows video images to be displayed by a device suitable for a user situation, and can enlarge opportunities for a user to be able to view video images. For example, suppose that a user is watching a video content program over the Internet with a television set in a room. When the user goes out and if the user switches the device that displays the video content program to a mobile phone, the user can enjoy the rest of the program also outdoors.
In this example where the display device is switched between a television set and a mobile phone, the receiving session of the video content program that the television set has been receiving is switched to the mobile phone. Such switching of a session between a plurality of different devices is called session mobility. While the above is an example of session mobility in video transmission, session mobility can also be applied to a session for transmitting audio or other data.
Properties required for session mobility include two characteristics, (a) speed and (b) continuity.
Speed refers to switching the display device as fast as possible. Speed is expressed by the length of time from when a user instructs to switch to when an application that uses the session operates in the switching destination device. In video transmission, for example, speed is expressed by the time from a switch instruction to when the video image is displayed on the switching destination device.
Continuity refers to the continuation of contents before and after switching. That is, when a device to display a video content program is switched to another device in the middle of the video content program, the switching destination device is required to display the continuation of the scene that the switching source device was displaying at the time of the switch instruction.
Japanese Patent Laid-Open Application No. 2002-368846 discloses, as a scheme to realize session mobility, a procedure for outputting contents accumulated in a mobile terminal to an external device via short-range wireless communication. Specifically, the mobile terminal searches for an external device, establishes connection with the found external device, and transfers the contents.